Two-stroke cycle diesel engine

Abstract

A two-stroke cycle diesel engine having: at least one two-stroke cycle power cylinder - piston assembly incorporating uniflow scavenging and having two horizontally opposed pistons, at least first and second scavenging ports and two crankcases which may perform crankcase compression; a pump assembly including at least one scavenging pump cylinder - piston assembly of the reciprocating type which is separate from and is driven by the power cylinder - piston assembly; and a scavenging air introducing device which introduces scavenging air compressed by the pump assembly to the first and the second scavenging ports through first and second passage systems, respectively; wherein the first passage system is interrupted before the pump assembly reaches its top dead center so that thereafter the scavenging air compressed by the pump assembly is all supplied to the second scavenging port which is adapted to generate strong swirl flows in the power cylinder when scavenging air at high pressure is supplied in a large amount.

We claim: 
     
       1. A two-stroke cycle diesel engine, comprising: at least one two-stroke cycle power cylinder-piston assembly having a power cylinder, having scavenging ports located near one axial end thereof and exhaust ports located near the other axial end thereof, two horizontally opposed power pistons, two crankcases, and two crank arms, and incorporating uniflow scavenging effected axially through said power cylinder from said scavenging ports to said exhaust ports, a scavenging pump device which supplied scavenging air; including at least one reciprocating pump cylinder-piston assembly having a pump cylinder and at least one pump piston, and which is separate from and is driven by said power cylinder-piston assembly; and scavenging air introducing device which introduces said scavenging air to said power cylinder, said scavenging air introducing device including a forced swirl generating device which generates a forced swirl of scavenging air in said power cylinder which rotates around the central axis of said power cylinder, wherein said scavenging air introducing device is adapted so as to perform a first stage of operation which effects scavenging without distinguished operation of said forced swirl generating device so that no strong swirl of scavenging air around the central axis of said power cylinder is generated and a second stage of operation which effects scavenging with distinguished operation of said forced swirl generating device so that a strong swirl of scavenging air around the central axis of said power cylinder is generated, wherein said power cylinder includes first and second scavenging ports, said scavenging air introducing device includes first and second passage systems which conduct scavenging air supplied from said scavenging pump device to said first and second scavenging ports, respectively, and said forced swirl generating device includes an air introducing device which gives swirl to scavenging air introduced into said power cylinder through said second passage system and a closer which isolates said first passage system from said pump cylinder-piston assembly before said pump cylinder-piston assembly reaches its top dead center, and wherein said second scavenging port is so arranged as to be opened at a phase point which is 5°-15° behind the phase point at which said first scavenging port is opened and which is not behind a phase point which is symmetric to the top dead center of said pump cylinder-piston assembly with respect to the line which connects the top dead center and the bottom dead center of said power cylinder-piston assembly, as viewed according to crank angle. 
     
     
       2. The engine of claim 1, wherein the bottom dead center of said pump cylinder-piston assembly is, as viewed according to crank angle, between 70°-90° in advance of the phase point at which said first scavenging port is opened, and the phase point at which said first passage system is isolated from said pump cylinder-piston assembly is, as viewed according to crank angle, between the first scavenging port opening phase point and a phase point at which said pump cylinder-piston assembly has 1/4 of its total stroke remaining before its top dead center. 
     
     
       3. The engine of claim 1, wherein said closer comprises said pump piston and a delivery port formed in the wall of said pump cylinder of said pump cylinder-piston assembly at a position which is traversed by said pump piston before said pump cylinder-piston assembly reaches its top dead center, said delivery port supplying scavenging air to said first passage system. 
     
     
       4. The engine of claim 1, wherein the ratio of the opening area of said second scavenging port to that of said first scavenging port is approximately 1/3. 
     
     
       5. The engine of any one of claims 1 & 2-4, wherein said scavenging pump device includes a reciprocating pump of crankcase compression type provided by at least one of said crankcases of said power cylinder-piston assembly, said at least one of said crankcases being connected to said first passage system, and the top dead center of said pump cylinder-piston assembly is in a delayed phase relative to the top dead center of said power cylinder-piston assembly, and wherein said closer comprises said pump piston and a valve port which opens in the wall of said crankcase and a valve which is incorporated in the crank arm and which selectively opens or closes said valve port in accordance with rotation of said crank arm. 
     
     
       6. The engine of any one of claims 1 & 2-4, wherein said scavenging pump device does not incorporate a pump of crankcase compression type, and the total stroke volume of said scavenging pump device is 1.3-2 times as large as the total stroke volume of said power cylinder-piston assembly. 
     
     
       7. The engine of any one of claims 1 & 2-4, wherein the engine comprises two power cylinder-piston assemblies which operate with a phase difference of 180° therebetween and one double-acting pump cylinder-piston assembly. 
     
     
       8. The engine of any one of claims 1 & 2-4, wherein said pump cylinder-piston assembly has two horizontally opposed pistons. 
     
     
       9. The engine of any one of claims 1 & 2-4, wherein said scavenging pump device includes a reciprocating pump of crankcase compression type provided by at least one of said crankcases of said power cylinder-piston assembly, said at least one of said crankcases being connected to said first passage system, and the top dead center of said pump cylinder-piston assembly is in a delayed phase relative to the top dead center of said power cylinder-piston assembly. 
     
     
       10. The engine of claim 9, wherein the total stroke volume of said scavenging pump device is 1.5-2.2 times as large as the total stroke volume of said power cylinder-piston assembly. 
     
     
       11. The engine of claim 9, wherein said reciprocating pump incorporates both crankcases of said power cylinder-piston assembly. 
     
     
       12. The engine of claim 11, wherein said first passage system includes passages which supply scavenging air compressed by said pump cylinder-piston assembly to both of said crankcases, and passages which connect said crankcases to said first scavenging port. 
     
     
       13. The engine of claim 11, wherein said first passage system comprises a first branch passage system which supplies scavenging air compressed by both said pump cylinder-piston assembly and one of the two crankcases to said power cylinder and a second branch passage system which supplies scavenging air compressed by the other of the two crankcases to said power cylinder. 
     
     
       14. The engine of claim 13, wherein said power cylinder further comprises a third scavenging port which is opened at a later phase point than said second scavenging port, said first branch passage system supplying scavenging air to said first scavenging port, while said second branch passage system supplies scavenging air to said third scavenging port. 
     
     
       15. The engine of claim 13, wherein said first branch passage system is directly connected to said first scavenging port, while said second branch passage system is connected to said first branch passage system at a position upstream of said first scavenging port, wherein the angle defined between said first and second branch passages on their upstream side is an acute angle.